Silicon based microchannel cooling and electrical package

ABSTRACT

A chip package includes: a substrate; a plurality of conductive connections in contact with the silicon carrier; a silicon carrier in a prefabricated shape disposed above the substrate, the silicon carrier including: a plurality of through silicon vias for providing interconnections through the silicon carrier to the chip stack; liquid microchannels for cooling; a liquid coolant flowing through the microchannels; and an interconnect to one or more chip stacks. The chip package further includes a cooling lid disposed above the chip stack providing additional cooling.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims priority from, U.S.application Ser. No. 13/365505 filed on Feb. 3, 2012; which applicationis itself a division of Ser. No. 12/062055, filed on Apr. 3, 2008; whichis incorporated by reference in its entirety herein.

STATEMENT REGARDING FEDERALLY SPONSORED-RESEARCH OR DEVELOPMENT

None.

INCORPORATION BY REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

None.

FIELD OF THE INVENTION

The invention disclosed broadly relates to the field of integratedcircuit packaging and more particularly relates to the field of coolingdevices for integrated circuits

BACKGROUND OF THE INVENTION

Current module cooling solutions remove heat primarily from the back ofa chip or chip stack, limiting the amount of heat which can be removed.Furthermore, it is difficult with conventional test fixturing to provideadequate cooling and interconnection to chips and chip stacks with finepitch interconnects during electrical testing.

Therefore, there is a need for a cooling device and process for coolingchips and chip stacks that overcomes the shortcomings of the prior art.

SUMMARY OF THE INVENTION

Briefly, according to an embodiment of the invention a method includesusing a prefabricated shape with a silicon carrier to form both liquidcooling and electrical interconnection for integrated circuits.

According to another embodiment of the present invention, a chip packagewith an integrated cooling structure includes: a substrate; a pluralityof conductive connections in contact with the silicon carrier; a siliconcarrier in a prefabricated shape disposed above the substrate, thesilicon carrier including: a plurality of through silicon vias forproviding interconnections through the silicon carrier to the chipstack; a first set of liquid microchannels for cooling; a liquid coolantflowing through the microchannels; and an interconnect to one or morechip stacks. The chip package further includes a cooling lid disposedabove the chip stack providing additional cooling. The cooling lidincludes: a temporary seal attaching the cooling lid to the siliconcarrier; and a second set of liquid microchannels aligned with the firstset.

BRIEF DESCRIPTION OF THE DRAWINGS

To describe the foregoing and other exemplary purposes, aspects, andadvantages, we use the following detailed description of an exemplaryembodiment of the invention with reference to the drawings, in which:

FIG. 1 shows a cross-section of a silicon carrier with multiple chipsand with integrated electrical interconnection and microchannel liquidcooling, according to an embodiment of the present invention;

FIG. 2 shows a silicon carrier with a chip and a chip stack and withintegrated electrical interconnection and microchannel liquid cooling,according to an embodiment of the present invention;

FIG. 3 shows one example of a silicon-based test head for chip stacktesting at chip level assembly, according to an embodiment of thepresent invention;

FIG. 4 shows an example of a silicon-based test head probe for chipstack testing at wafer level, according to an embodiment of the presentinvention;

FIG. 5 shows a silicon-based carrier providing cooling to both the topand bottom of a chip, according to an embodiment of the presentinvention;

FIG. 6 shows an example of a silicon-based carrier on a segmentedplatform, according to an embodiment of the present invention;

FIG. 7 shows another example of a silicon-based test head for chip stacktesting at chip level assembly, according to an embodiment of thepresent invention; and

FIG. 8 shows a flow chart of a method for producing a silicon-based chippackage, according to an embodiment of the present invention.

While the invention as claimed can be modified into alternative forms,specific embodiments thereof are shown by way of example in the drawingsand will herein be described in detail. It should be understood,however, that the drawings and detailed description thereto are notintended to limit the invention to the particular form disclosed, but onthe contrary, the intention is to cover all modifications, equivalentsand alternatives falling within the scope of the present invention.

DETAILED DESCRIPTION

We describe an integrated silicon (Si) carrier that provides bothmicrochannel cooling and electrical interconnections for integratedcircuits. The silicon carrier includes electrical through vias,electrical wiring and an interconnection to chips made by means ofmetallic conductors such as solder and/or copper. The interconnectionsprovide both electrical and thermal transport.

Additional thermal transport may be added, if required, by means ofalternate or additional thermal paths off the chip or chip stack. Thecarrier can function as a permanent package to support chips and/or chipstacks as well as provide means for testing for known good chips wherethe silicon base acts to provide power and cooling.

A method according to an embodiment of the invention provides a way toremove heat effectively from a silicon carrier, which when used withsmall, high-conductivity balls or interconnects in the range of sizefrom about 2.0 to 20 microns in diameter (for very high densityinterconnections) to about 50 to 100 microns in diameter (for lowerdensity interconnections) as described herein provides an effective wayto remove heat from the front as well as from the back of a chip or chipstack. This is useful both for chip testing and for chip operation in afinal application.

The interconnections between the silicon carrier and the chips or chipstacks may have one or more size pads, or interconnections, such thatsmall size interconnections may provide a means for electricalinterconnections of signals, power and grounds (as well as enhancethermal conduction) and there may be other pads or large areainterconnections which serve as an alternate means for heat transfer andmay also be used for electrical interconnection. This method forfabricating the integrated carrier simplifies the methodology forassembly, test, and also reduces the hardware required in moduleassembly, as well as rework.

We describe a silicon package with electrical through silicon vias (TSV)and liquid cooling for one or more chips mounted on the surface and alsofor many layers of chips stacked with cooling only on periodic layers.The reason for this is that the use of liquid generally increases thethickness of the silicon layer and thus increases the electrical linkpath in that layer and this is not desirable for a high density stack ofchip with high bandwidth interconnections.

Referring now in specific detail to the drawings, and particularly FIG.1, there is illustrated an integrated circuit package according to anembodiment of the present invention. FIG. 1 is a simplified schematic ofthe structure of a silicon-based package. Shown is a cross-section of apackage 100 that provides electrical interconnection for power (voltageand ground to the silicon chip) and for signals to the chips 1 and 2,between chips 1 and 2 on the silicon carrier 120, and off the siliconcarrier 120 and provides for liquid cooling of one or more chips 1 and 2on the silicon carrier 120. Note that for purposes of this disclosure,we use the term “chip” to encompass a single chip, chip stack, wafer, orstack of wafers.

The liquid cooling channels 108 (shown as a wave pattern) can befabricated to permit liquid cooling across the silicon package 105. Inaddition, through-silicon-vias (TSV) 110 are introduced which providevertical electrical interconnections. Note the through-silicon-vias 110may take advantage of electrical isolation from the silicon carrier 120by means of a dielectric layer between the silicon and a conductor, suchas Tungsten (W) or Copper (Cu).

The silicon carrier 120 may also provide electrical wiring for a highbandwidth interconnection between chips 1 and 2, may provide integrateddecoupling capacitors to support low inductance and close proximitycapacitors to chips 1 and 2, and may provide active and/or passivecircuits for voltage regulation, power inversion and/or other functions.

The silicon package 105 uses small, heat conductive interconnects 112such as balls preferably made from copper or solder between the chipsand the carrier 120. The balls 112 provide thermal as well as electricaltransport. Additionally, balls 122 placed between the carrier 120 andthe substrate 102 serve to further provide thermal and electricaltransport.

The silicon carrier 120 may be mounted on another substrate 102 forimproved mechanical integrity as well as providing a means forintegration into a module, onto a board or socket by use of a ball gridarray (BGA) 140, column grid array (CGA) or land grid array (LGA)interconnection. Cooling of the chips 1 and 2 may be done by means ofheat removal from the back of the chips 1 and 2, by means of liquidcooling for heat removal from the silicon carrier, or by a combinationof both.

Interconnections for liquid to remove heat from the silicon carrier 120may be achieved by means of a connector, cap or lid (shown in FIG. 3)disposed over the chips 1 and 2 which connects by means of an adhesive(such as epoxy-based or silicon-based adhesive) or other means tochannels, holes and or other liquid conduits created in the siliconcarrier 120. A thermal enhancement material such as a thermal interfacematerial (TIM), thermally conductive gel, solder or alternate thermalenhancement structure and method may be used to transfer heat from thechips 1 and 2 to the lid, cap or module, and/or between chips and thesilicon package.

The TSV 110 and liquid channels 108 in the silicon carrier 120 may beformed by means of deep reactive ion etching or other means known in theart. In addition, the silicon package 100 may provide a means for notonly electrical and thermal cooling but may also provide a means foroptical interconnections (not shown) on or off module by use of verticaland/or horizontal channels or holes or other optical conduits.

FIG. 2 shows a schematic cross-section of a silicon-based package 200featuring integrated electrical and microchannel liquid cooling ofstacked chips. The package of FIG. 2 provides electrical interconnectionfor power (voltage and ground to the silicon chips) and for signals tothe chips and/or chip stacks, between chips and/or chip stacks, and offthe silicon substrate and provides for liquid cooling of one or morechips and/or chip stacks on the silicon substrate 102.

Referring to FIG. 3 there is shown a silicon-based test platformsubstrate with an integrated cooling structure. This provides sockettesting for chip stacks or chip stacks on a module. Liquid coolingprovides cooling during test by means of liquid flow through the lid 322and silicon carrier 120. Note the temporary seal between the lid 322 andthe silicon package may be a rubber or polymer “O” ring to seal a liquidconnection between the lid 322 and the silicon carrier 120. An adhesivemay be used from the silicon carrier 120 to the substrate 102 forimproved mechanical integrity of the silicon package 105. Power, ground,and signals for testing can be provided with active circuits in thesilicon package 105 and/or by means of electrical interconnectionsthrough the supporting substrate and/or board interconnections.

Referring to FIG. 4 there is shown a silicon test head probe thatprovides means for electrical test and cooling of wafers or wafer stackswith integrated liquid cooling in a silicon based package.

Referring to FIG. 5 there is shown a silicon-based package 505 which canprovide electrical and liquid cooling to one or more chips 1 and 2(shown) from both sides of the chips 1 and 2. The structure 505 can alsoprovide electrical and liquid cooling to chips and/or chip stacks whereliquid cooling may be critical in cooling chip stacks from the top andbottom of the chip stacks as well as power delivery and signaltransmission may be critical from one or both top and bottom of the chipstacks.

Referring to FIG. 6 there is shown a structure wherein a silicon-basedpackage 605 provides a segmented platform to provide electrical power,voltage and signal transmission to one or more chip stacks 601 as wellas liquid cooling for the chip stacks 601. These units 605 may bestacked for power delivery, signal transmission and cooling within thestacked chips and package structures, as shown. In addition, but notshown, optical interconnections may also be provided by means of thesilicon package 605.

Referring to FIG. 7 there is shown an example of a test head, probe orsocket which can be utilized to test stacked chips 1 and 2, along withsilicon packages 705 which provide electrical power, signal transmissionand cooling for the assemblies in stacked configurations.

Referring to FIG. 8 there is shown a high-level flow chart 800 of amethod for producing a coolant device according to an embodiment of thepresent invention. In step 810 the silicon carrier 120 is fabricatedwith through-silicon-vias 110 and microchannels 108 for liquid coolant.The through-silicon-vias 110 can accommodate electrical conduits oroptical interconnects. The vias 110 run through the carrier to makecontact with the chip 1.

Next, in step 820 the substrate 102 is fabricated. Note the order ofsteps 810 and 820 can be switched. In step 840 we affix the substrate102 to the silicon carrier 120 and affix chips to the silicon carrier.

In step 850, once the chips are positioned, we place an additionalcoolant device above them. This coolant device may be a cap 322 oranother carrier 520. Note that the additional carrier 520 should also bepre-fabricated with through-silicon-vias 110 and microchannels 108 inorder to further enhance cooling. Step 850 may be repeated withadditional layers of carrier 520, chip 1, and additional carrier 520.

In step 860 we place a ball array 140 between the substrate 102 and aprinted circuit board or other surface.

While typically only about 5% of the heat from the chip travels from thechip through the C4's (controlled collapse chip connections) into thefirst level package, it is possible to greatly increase the amount ofheat removed from the front of the chip by using smaller metal balls 112with better thermal conductivity and by providing a way to remove heatfrom the first level package. For example, if there were a 25% coverageof copper balls 25 microns high between the chip and the first levelpackage, the area normalized thermal resistance (Rth) would be

Rth=25×10−6 m/(0.25×390 W/m−K)=0.25 K−mm2/W

Even after adding the thermal resistance of the chip wiring/insulationlayers, the thermal resistance could be less than or comparable to thatfor removing heat from the back of the chip. This invention describes away to remove heat effectively from a silicon carrier, which when usedwith small, high-conductivity balls as described here, can provide a wayto effectively remove heat from the front of the chip as well as fromthe back. This can be useful both for chip testing and for chipoperation in a final application.

Therefore, while there has been described what is presently consideredto be the preferred embodiment, it will understood by those skilled inthe art that other modifications can be made within the spirit of theinvention.

1. A chip package with an integrated cooling structure comprising: asubstrate; a plurality of small metallic connections in contact with thesubstrate; a silicon carrier for a chip stack in a prefabricated shapedisposed above the substrate, the silicon carrier comprising: aplurality of through silicon vias for providing interconnections throughthe silicon carrier to the chip stack; a first set of liquidmicrochannels for cooling; a liquid coolant flowing through themicrochannels; and an array of small, highly thermally conductivemetallic connections attaching one or more chip stacks; and a coolinglid disposed above the chip stack, said cooling lid comprising: atemporary seal attaching the cooling lid to the silicon carrier; and asecond set of liquid microchannels for cooling, said second set alignedwith the first set at each end of the cooling lid such that liquid isable to flow between said cooling lid and the silicon carrier withoutimpedance when said cooling lid is attached.
 2. The chip package ofclaim 1 wherein the interconnection to the chip stack provides bothelectrical and thermal transport and comprises metallic conductors. 3.The chip package of claim 1 wherein the plurality of through siliconvias are etched into the silicon carrier.
 4. The chip package of claim 1wherein the first set of liquid microchannels is etched into thesilicon.
 5. The chip package of claim 1 further comprising a dielectriclayer in the silicon carrier disposed between the silicon and theinterconnection metal.
 6. The chip package of claim 1 wherein theplurality of small, high heat conductive metallic connections comprisean array selected from a group consisting of: copper to copperinterconnections; metallic interconnections; solder micro-joints;controlled collapse chip connections; thin height, large areaconnections; an array of connections of equal size; and a combination ofsmaller thin connections and large area thin interconnections.
 7. Thechip package of claim 1 wherein the substrate is attached to a card,board, or other surface with an area array selected from a groupconsisting of: a ball grid array; a column grid array; a pin grid array;a land grid array; and a high density connector.
 8. The chip package ofclaim 1 further comprising a thermal interface material disposed betweenthe cooling lid and the chip stack to transfer heat from the chip stack.9. The chip package of claim 8 wherein the thermal interface material isfurther disposed between the chip stack and the silicon carrier.
 10. Thechip package of claim 1 wherein the plurality of through silicon viasprovide electrical interconnections.
 11. The chip package of claim 10wherein the electrical interconnections are vertical.
 12. The chippackage of claim 1 wherein the cooling lid may also provide electricalinterconnection to the chip stack for power delivery and signalinterconnection.
 13. The chip package of claim 1 wherein the pluralityof through silicon vias provide optical interconnections.
 14. The chippackage of claim 1 wherein the temporary seal comprises an o-ringsealing a liquid connection between the cooling lid and the siliconcarrier.
 15. The chip package of claim 14 wherein the o-ring is formedof rubber.
 16. The chip package of claim 1 further comprising anadhesive applied between the silicon carrier and the substrate, saidadhesive providing improved mechanical integrity of said chip package.17. The chip package of claim 1 further comprising: active circuits inthe silicon carrier providing power, ground and signals for testing.